Relative time division for network coding

ABSTRACT

A base station serves multiple user terminals via a relay node in a cell of a wireless network. The base station includes a time division scheme selection unit that selects a time division scheme from multiple time division schemes that optimizes a parameter associated with network coding of data transmitted between the multiple user terminals and the base station via the relay node. The base station further includes a transmission allocation unit that allocates uplink and/or downlink transmission intervals and interval lengths, based on the selected time division scheme, to each of the multiple user terminals and to the relay node. The base station also includes a notification message unit that notifies the multiple user terminals and the relay node of their respective transmission interval and interval length allocation.

TECHNICAL FIELD

Implementations described herein relate generally to relaying inwireless communication systems and, more particularly, to the relativetime division of transmission phases during network coding in wirelesscommunication systems.

BACKGROUND

A striving force in the development of wireless/cellular communicationnetworks and systems has been to provide increased network coverageand/or to support higher data rates. At the same time, the cost aspectof building and maintaining the system is of great importance and isexpected to become even more so in the future. As data rates and/orcommunication distances are increased, the problem of increased batteryconsumption is another area of concern. Until recently, the maintopology of wireless communication systems has been fairly unchanged,including the three existing generations of cellular networks. Thetopology of existing wireless communication systems is characterized bya cellular architecture that includes fixed radio base stations andmobile stations as the only transmitting and receiving entities in thenetworks typically involved in a communication session.

A technique for introducing macro-diversity in a received signalinvolves the use of relaying systems where information sent to anintended destination may be conveyed through various routes and combinedat the destination. Each route may consist of one or more hops utilizingthe relay nodes. In addition, the destination may receive the directsignal from the source. Cooperative relaying systems can be divided intonumerous categories based on desired parameters. For instance, the waythe signal is forwarded and encoded at the relay station can beclassified into two categories: amplify-and-forward anddecode-and-forward. In the amplify-and-forward case, the relays simplyamplify and forward the received signal. In the decode-and-forward case,the relays demodulate and decode the signal prior to re-encoding andre-transmission.

Present day communication networks, described above, share the samefundamental principle of operation: the information or packet sent froma source to a destination is transported independently from otherinformation sent from another source to the same destination. Routers,repeaters and relays simply forward the data to the destination. Incontrast to those communication networks, network coding (NC) is a newarea of networking, in which data is manipulated inside the network(e.g., at an intermediate node, N) to improve throughput, delay androbustness. In particular, NC allows the intermediate nodes to recombineseveral input packets into one or several output packets. At theintermediate node (referred to as the network coding node) some type oflinear coding can be performed on the packets present at the networkcoding node, and the resulting encoded packet can be broadcast fordifferent recipients simultaneously instead of transmitting each packetseparately.

In wireless communications, network coding can be divided into twoschemes: analog network coding and digital network coding. In analognetwork coding, coding may be performed at the signal level. This mayconsist of letting the analog signals add up in the air throughsimultaneous transmissions (i.e., by letting two signals interfere witheach other intentionally). The coding (i.e., signal addition) may thenoccur at the intermediate relay node and both decode-and-forward andamplify-and-forward techniques may be employed in analog network coding.In digital network coding, coding may be performed at the packet level,with encoding being performed on the bits of the packets. The encodingmay include XOR operations, or other types of bit operations, beingperformed on the bits of the packets. Digital network coding may beperformed only with decode-and-forward relays, since the network codingnode needs to possess decoding capabilities. When network coding isapplied to a wireless relay network, a relay node may play the role of anetwork coding node.

SUMMARY

Exemplary embodiments described herein provide techniques for dividingand allocating the transmission resources (e.g., uplink or downlink) inthe case where at least two user terminals transmit their data to acertain destination through a relaying node. Transmission intervals andinterval lengths (e.g., in a cell of a wireless network) may beallocated to user terminals, and to a relay node involved in the networkcoding of data transmissions to a base station, based on the selectionof a time division scheme from multiple time division schemes. Varioustime division schemes may be used herein for dividing the transmissionintervals and interval lengths, and for allocating the time dividedintervals to the user terminals and the relay node. Such time divisionschemes may include, but are not limited to, a time division scheme thatattempts to achieve “fairness-per-node,” a time division scheme thatattempts to achieve “fairness-per-user terminal,” and a time divisionscheme that attempts to achieve equal delay per user terminal. Any ofthese time division schemes or other time division schemes, either bythemselves or in combination, may be selected to allocate transmissionintervals and interval lengths to user terminals transmitting data tothe relay node for network coding. Other time division schemes that maybe selected include schemes based on channel quality measures ofdifferent links in the system. For example, the other time divisionschemes may be based on channel quality measures associated with thelinks between the user terminals and the relay node, between the relaynode and the base station and/or between the user terminals and the basestation.

In some implementations, a cost function-based algorithm may be used tooptimize a certain parameter(s) associated with the network codingprocess through the selection of a time division scheme from themultiple different time division schemes. Implementations describedherein, thus, provide network coding aware time division schemes thatcan control the fairness of the system while being able to maximize aperformance measure of interest through design of a cost function.Implementations described herein further increase system spectralefficiency and reduce system outages, and can be combined with userterminal grouping algorithms and relay node selection algorithms tooptimize scheduling (e.g., throughput, fairness) for a network codingsystem.

According to one aspect, a method may include determining qualities oflinks between user terminals and a base station in a wireless networkand selecting a time division scheme from multiple time division schemesbased on the determined qualities of the links. The method may furtherinclude allocating transmission intervals and interval lengths, based onthe selected time division scheme, to each of the user terminals and toa relay node that relays data transmissions from the user terminals tothe base station. The method may also include notifying the userterminals and the relay node of their respective allocated transmissionintervals and interval lengths.

According to a further aspect, a base station that serves multiple userterminals via a relay node in a cell of a wireless network may include atime division scheme selection unit configured to select a time divisionscheme from multiple time division schemes that optimizes a parameterassociated with network coding of data transmitted between the multipleuser terminals and the base station via the relay node. The base stationmay further include a transmission allocation unit configured toallocate uplink and/or downlink transmission intervals and intervallengths, based on the selected time division scheme, to each of themultiple user terminals and to the relay node. The base station may alsoinclude a notification message unit configured to notify the multipleuser terminals and the relay node of their respective transmissioninterval and interval length allocation.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more embodiments of theinvention and, together with the description, explain the invention. Inthe drawings:

FIG. 1 illustrates an exemplary communications system in whichembodiments described herein may be implemented;

FIG. 2 illustrates an exemplary implementation in which a network of thesystem of FIG. 1 includes a Public Land Mobile Network (PLMN);

FIG. 3A illustrates exemplary components of the base station of FIG. 1;

FIG. 3B illustrates exemplary functional components of the base stationof FIG. 1;

FIG. 4A illustrates exemplary components of a user terminal of FIG. 1;

FIG. 4B illustrates an exemplary implementation of the user terminal ofFIG. 4A where the user terminal is a cellular radiotelephone;

FIG. 5 depicts details of the network coding and relaying of datatransmissions from a group of user terminals by a selected relay node toa base station at specified transmission time intervals;

FIG. 6 illustrates a “fair-per-node” time division scheme according toan exemplary embodiment;

FIG. 7 illustrates a “fair-per-user terminal” time division schemeaccording to an exemplary embodiment;

FIG. 8 is a flowchart that illustrates exemplary operations associatedwith selecting a time division scheme for time dividing a transmissionresource and allocating transmission intervals and interval lengths touser terminals and a relay node involved in network coding based on theselected time division scheme; and

FIG. 9 is an exemplary messaging diagram associated with the exemplaryoperations of FIG. 8.

DETAILED DESCRIPTION

The following detailed description of the invention refers to theaccompanying drawings. The same reference numbers in different drawingsmay identify the same or similar elements. Also, the following detaileddescription does not limit the invention.

FIG. 1 illustrates an exemplary communications system 100 that mayinclude multiple user terminals (UT) 110-1 through 110-N connected to anetwork 120 via multiple relay nodes 130-1 through 130-P and a basestation 140. UTs 110-1 through 110-N may communicate 150 with devices160-1 through 160-M via relays 130-1 through 130-P and base station 140(and other components of network 120 not shown in FIG. 1). Thus, relaynodes 130-1 through 130-P and base station 140 may function asintermediate components of communications system 100 that may be used tofacilitate end-to-end communication between UTs 110-1 through 110-N anddevices 160-1 through 160-M.

UTs 110-1 through 110-N may include cellular radiotelephones, personaldigital assistants (PDAs), Personal Communications System (PCS)terminals, laptop computers, palmtop computers, or any other types ofdevices or appliances that include a communication transceiver thatpermits the device to communicate with other devices via a wirelesslink. A PCS terminal may combine a cellular radiotelephone with dataprocessing, facsimile and data communications capabilities. A PDA mayinclude a radiotelephone, a pager, an Internet/intranet access device, aweb browser, an organizer, calendars and/or a global positioning system(GPS) receiver. UTs 110-1 through 110-N may be referred to as “pervasivecomputing” devices.

Relay nodes 130-1 through 130-P may include wireless nodes that receivedata transmissions from multiple ones of UTs 110-1 through 110-N andnetwork code (described further below) and relay the received datatransmissions to base station 140. The network coding performed by relaynodes 130-1 through 130-P may include analog or digital network coding.The digital network coding typically involves linearly combining datafrom a group of user terminals, such as, for example, XOR bitwiseencoding, Reed Solomon encoding, modulus encoding, or other types ofoperations for combining data bits from different user terminals of agroup of user terminals.

Devices 160-1 and 160-M may include similar devices to UTs 110-1 through110-N and, in some implementations, may additionally include telephones(e.g., Plain Old Telephone system (POTs) telephones) that are connectedto a Public Switched Telephone Network (PSTN).

Network(s) 120 may include one or more networks of any type, including alocal area network (LAN); a wide area network (WAN); a metropolitan areanetwork (MAN); a telephone network, such as a PSTN or a PLMN; asatellite network; an intranet, the Internet; or a combination ofnetworks. The PLMN(s) may further include a packet-switched sub-network,such as, for example, General Packet Radio Service (GPRS), CellularDigital Packet Data (CDPD), or Mobile IP network.

FIG. 2 illustrates an example of system 100 of FIG. 1, where network 120includes a PLMN 200. As shown in FIG. 2, UTs 110-1 and 110-N and device160 may include cellular radiotelephones.

PLMN 200 may include one or more base station controllers (BSCs) 205-1through 205-Y (alternatively called “radio network controllers” (RNCs)in some implementations), multiple base stations (BSs) 140 and 210-1through 210-X along with their associated antenna arrays, one or moremobile switching centers (MSCs), such as MSC 215, and one or moregateways (GWs), such as GW 220. PLMN 200 may additionally includecomponents (not shown) for connecting PLMN 200 to a packet-switchednetwork, such as a Packet Data Network (PDN), such that UTs 110-1through 110-N and device 160 can send or receive packet-switched datafrom the PDN. The components for connecting PLMN 200 to the PDN mayinclude a Serving GPRS Support Node (SGSN) and a Gateway GPRS SupportNode (GGSN) (not shown).

Base stations 140 and 210-1 through 210-X may format the datatransmitted to, or received from, the antenna arrays in accordance withexisting techniques and may communicate with BSCs 205-1 through 205-Y orwith a device, such as device 160. Among other functions, BSCs 205-1through 205-Y may route received data to either MSC 215 or a basestation (e.g., BSs 140 or 210-1 through 210-X). MSC 215 may routereceived data to BSC 205-1, 205-Y, or GW 220. GW 220 may route datareceived from an external domain (not shown) to an appropriate MSC (suchas MSC 215), or from an MSC to an appropriate external domain. In oneimplementation, the external domain may include a different PLMN or aPSTN.

FIG. 3A illustrates an exemplary implementation of BS 140. Base stations210-1 through 210-X may be similarly configured. BS 140 may include atransceiver 305, a processing unit 310, a memory 315, an interface 320and a bus 325.

Transceiver 305 may include transceiver circuitry for transmittingand/or receiving symbol sequences using radio frequency signals via oneor more antennas. Processing unit 310 may include a processor, amicroprocessor, or processing logic that may interpret and executeinstructions. Processing unit 310 may perform all device data processingfunctions. Memory 315 may provide permanent, semi-permanent, ortemporary working storage of data and/or instructions for use byprocessing unit 310 in performing device processing functions. Memory315 may include read only memory (ROM), random access memory (RAM),large-capacity storage devices, such as a magnetic and/or opticalrecording medium and its corresponding drive, and/or other types ofmemory devices. Interface 320 may include circuitry for interfacing witha link that connects to a BSC (e.g., BSC 205-1 or BSC 205-Y). Bus 325may interconnect the various components of BS 140 to permit thecomponents to communicate with one another.

The configuration of components of BS 140 illustrated in FIG. 3A is forillustrative purposes only. Other configurations with more, fewer, or adifferent arrangement of components may be implemented.

FIG. 3B illustrates a functional diagram of base station 140 accordingto an exemplary implementation. The various functional components shownin FIG. 3B may be implemented by processing unit 310, memory 315,transceiver 305, and possibly other components of base station 140. Basestation 140 may include a link quality analysis unit 330, a timedivision scheme selection unit 340, an uplink/downlink transmissionallocation unit 345, and a notification message unit 350.

Link quality analysis unit 330 may analyze link quality information thatmay be received from UTs 110-1 through 110-N, received from a relay node130, and/or may be measured at base station 140. The link qualityinformation may include, for example, link quality informationassociated with the direct radio channel links between UTs 110-1 through110-N and base station 140, link quality information associated with thelinks between UTs 110-1 through 110-N and relay node 130, and linkquality information associated with the link between relay node 130 andbase station 140.

Time division scheme selection unit 340 may select a time divisionscheme to use for allocating transmission intervals and interval lengths(i.e., time slots and their respective lengths). For example, in acellular system, the selected time division scheme may allocatetransmission intervals and interval lengths on the uplink and/ordownlink. The time division schemes may include, among other timedivision schemes, a time division scheme to achieve “fairness-per-node,”a time division scheme to achieve “fairness-per-user terminal,” and atime division scheme to achieve “equal delay” per user terminal. Any ofthese time division schemes, either by themselves or in combination, maybe selected to allocate uplink transmission intervals and intervallengths to each of UTs 110-1 through 110-N and to relay node 130 for thenetwork coding. As further described below, a cost function basedalgorithm may be used to optimize certain desired performance measuresusing one or more selected time division schemes. The“fairness-per-node” and “fairness-per-user terminal” time divisionschemes are described in more detail below.

Uplink/downlink transmission allocation unit 345 may allocate uplinkand/or downlink transmission intervals and interval lengths based on thetime division scheme selected by time division scheme selection unit340. Allocation of transmission intervals and interval lengths, for theexemplary “fair-per-node” and “fair-per-user terminal” time divisionschemes are described in further detail below with respect to FIGS. 6and 7.

Notification message unit 350 may construct one or more notificationmessages that may inform the selected relay node 130 and the userterminals 110-1 through 110-N of the allocated transmission intervalsand interval lengths. A single notification message may be constructedand sent to relay node 130 for relaying on to UTs 110-1 through 110-N,or multiple notification messages may be constructed that can be sent torelay node 130 and directly to each of UTs 110-1 through 110-N.

FIG. 4A illustrates exemplary components of a UT 110. Relays 130-1through 130-P may be similarly configured. UT 110 may include atransceiver 405, a processing unit 410, a memory 415, an input device(s)420, an output device(s) 425, and a bus 430.

Transceiver 405 may include transceiver circuitry for transmittingand/or receiving symbol sequences using radio frequency signals via oneor more antennas. Transceiver 405 may include, for example, a RAKE or aGRAKE receiver. Processing unit 410 may include a processor,microprocessor, or processing logic that may interpret and executeinstructions. Processing unit 410 may perform all data processingfunctions for inputting, outputting, and processing of data includingdata buffering and device control functions, such as call processingcontrol, user interface control, or the like.

Memory 415 may provide permanent, semi-permanent, or temporary workingstorage of data and instructions for use by processing unit 410 inperforming device processing functions. Memory 415 may include ROM, RAM,large-capacity storage devices, such as a magnetic and/or opticalrecording medium and its corresponding drive, and/or other types ofmemory devices. Input device(s) 420 may include mechanisms for entry ofdata into UT 110. For example, input device(s) 420 may include a key pad(not shown), a microphone (not shown) or a display unit (not shown). Thekey pad may permit manual user entry of data into UT 110. The microphonemay include mechanisms for converting auditory input into electricalsignals. The display unit may include a screen display that may providea user interface (e.g., a graphical user interface) that can be used bya user for selecting device functions. The screen display of the displayunit may include any type of visual display, such as, for example, aliquid crystal display (LCD), a plasma screen display, a light-emittingdiode (LED) display, a cathode ray tube (CRT) display, an organiclight-emitting diode (OLED) display, etc.

Output device(s) 425 may include mechanisms for outputting data inaudio, video and/or hard copy format. For example, output device(s) 425may include a speaker (not shown) that includes mechanisms forconverting electrical signals into auditory output. Output device(s) 425may further include a display unit that displays output data to theuser. For example, the display unit may provide a graphical userinterface that displays output data to the user. Bus 430 mayinterconnect the various components of UT 110 to permit the componentsto communicate with one another.

The configuration of components of UT 110 illustrated in FIG. 4A is forillustrative purposes only. Other configurations with more, fewer, or adifferent arrangement of components may be implemented.

FIG. 4B illustrates an exemplary implementation of UT 110 in which UT110 includes a cellular radiotelephone. As shown in FIG. 4B, thecellular radiotelephone may include a microphone 435 (e.g., of inputdevice(s) 420) for entering audio information into UT 110, a speaker 440(e.g., of output device(s) 425) for providing an audio output from UT110, a keypad 445 (e.g., of input device(s) 420) for manual entry ofdata or selection of device functions, and a display 450 (e.g., of inputdevice(s) 420 or output device(s) 425) that may visually display data tothe user and/or which may provide a user interface that the user may useto enter data or to select device functions (in conjunction with keypad445).

FIG. 5 illustrates the performance of network coding of data from agroup of user terminals at a relay node and relaying of the networkcoded data to a base station. As shown in FIG. 5, user terminal 110-1may transmit 510 data b₁ during transmission time interval T₁ to relaynode 130. Relay node 130 may be selected from relay nodes 130-1 through130-P of FIG. 1 based on a selection scheme not described herein. Userterminal 110-N may also transmit 520 data b₂ during transmission timeinterval T₂ to relay node 130. Subsequent to receipt of data b₁ and b₂,relay node 130 may perform network coding 530 on the data, and then mayrelay/transmit 540 the network coded data to base station 140 duringtransmission time interval T₃. In the exemplary implementation depictedin FIG. 5, relay node 130-1 is depicted as using Exclusive OR operations(XOR-⊕) to network code the data b₁ and b₂ received from UTs 110-1 and110-N. In other implementations, different network coding schemes may beused.

As described herein, the relative time division of transmission phases(i.e., transmission time intervals or time slots) in a wireless networkcoding system may be achieved according to various time divisionschemes. For example, assuming that there are two user terminals beingnetwork coded, the various time division schemes may allocate differenttransmission intervals and interval lengths (e.g., uplink and/ordownlink) for each of the time intervals T₁, T₂ and T₃ shown in FIG. 5.For example, one time division scheme may achieve “fairness-per-node.”Another time division scheme may attempt to achieve “fairness-per-userterminal.” A further time division scheme may attempt to achieve equaldelay per user terminal. Any of these time division schemes or othertime division schemes, either by themselves or in combination, may beselected to allocate uplink transmission intervals and interval lengthsto each of UTs 110-1 through 110-N and to relay node 130. The other timedivision schemes may include schemes based on channel quality measuresof different links in the system. For example, the other time divisionschemes may be based on channel quality measures associated with thelinks between the user terminals and the relay node, between the relaynode and the base station and/or between the user terminals and the basestation.

As further described below, a cost function based algorithm may be usedto optimize certain desired performance measures using one or moreselected time division schemes.

Signal-to-Noise and Interference Ratios (SINR) equations associated withthe network coding transmissions shown in FIG. 5 may be derived and usedto demonstrate how different time division schemes lead to differentcapacity equations that may be used to optimize certain desiredperformance measures. Assume that during T₁, a first user terminal(e.g., user terminal 110-1) transmits, and its signal is received atbase station 140 and relay 130. The signal received after OrthogonalFrequency Division Multiplexing (OFDM) demodulation at base station 140for the k^(th) sub-carrier of user terminal 1 may be expressed as:

$\begin{matrix}{{y_{1}^{(1)}(k)} = {{{H_{1,1}(k)}{s_{1,1}(k)}} + {\sum\limits_{i = 2}^{N_{b}}\;{{H_{i,1}(k)}{s_{i,1}(k)}}} + {w_{1}(k)}}} & {{Eqn}.\mspace{14mu}(1)}\end{matrix}$

where:

H_(i,j)(k) is the radio channel between the transmitter of the j^(th)user terminal of BS i and the receiver of BS 1,

s_(i,j)(k) is the modulated signal of the j^(th) user terminal in BS i,

w₁(k) is the thermal noise, and

N_(b) is the number of base stations in the system.

The signal received at relay node 130 after T₁ may be expressed as:

$\begin{matrix}{{y_{r,1}^{(1)}(k)} = {{{H_{r,1,1}(k)}{s_{1,1}(k)}} + {\sum\limits_{i = 2}^{N_{b}}\;{{H_{r,i,1}(k)}{s_{i,1}(k)}}} + w_{r,1}}} & {{Eqn}.\mspace{14mu}(2)}\end{matrix}$

where H_(r,i,j) is the radio channel between the transmitter of thej^(th) user terminal of BS i and the receiver of the active relay nodeof BS 1.

The SINR at base station 140 after T₁, Γ₁ may be expressed as:

$\begin{matrix}{\Gamma_{1} = \frac{{H_{1,1}}^{2}p_{1,1}}{{\sum\limits_{i = 2}^{N_{b}}\;{{H_{i,1}}^{2}p_{i,1}}} + \sigma_{1}^{2}}} & {{Eqn}.\mspace{14mu}(3)}\end{matrix}$

where p_(i,j) is the transmitted power of the j^(th) user terminal of BSi.

The SINR for user terminal 1 at relay node 130 after T₁ is denoted asΓ_(r,1) and may be expressed as:

$\begin{matrix}{\Gamma_{r,1} = \frac{{H_{r,1,1}}^{2}p_{1,1}}{{\sum\limits_{i = 2}^{N_{b}}\;{{H_{r,i,1}}^{2}p_{i,1}}} + \sigma_{r,1}^{2}}} & {{Eqn}.\mspace{14mu}(4)}\end{matrix}$Similarly, the signal received at base station 140 after user terminal 2(e.g., UT 110-N) has transmitted during T₂ may be expressed as:

$\begin{matrix}{{y_{1}^{(2)}(k)} = {{{H_{1,2}(k)}{s_{1,2}(k)}} + {\sum\limits_{i = 2}^{N_{b}}{{H_{i,2}(k)}{s_{i,2}(k)}}} + w_{1}}} & {{Eqn}.\mspace{14mu}(5)}\end{matrix}$The signal received at relay node 130 after T₂ may be expressed as:

$\begin{matrix}{{y_{r,1}^{(2)}(k)} = {{{H_{r,1,1}(k)}{s_{1,2}(k)}} + {\sum\limits_{i = 2}^{N_{b}}{{H_{r,i,2}(k)}{s_{i,2}(k)}}} + w_{r,2}}} & {{Eqn}.\mspace{14mu}(6)}\end{matrix}$The SINR at base station 140 after T₂, Γ₂, may be expressed as

$\begin{matrix}{\Gamma_{2} = \frac{{H_{1,2}}^{2}p_{1,2}}{{\sum\limits_{i = 2}^{N_{b}}\;{{H_{i,2}}^{2}p_{i,2}}} + \sigma_{2}^{2}}} & {{Eqn}.\mspace{14mu}(7)}\end{matrix}$The SINR for user terminal 2 (e.g., UT 110-N) at relay node 130 after T₂is denoted as Γ_(r,2) and may be expressed as:

$\begin{matrix}{\Gamma_{r,2} = \frac{{H_{r,1,2}}^{2}p_{1,2}}{{\sum\limits_{i = 2}^{N_{b}}\;{{H_{r,i,2}}^{2}p_{i,2}}} + \sigma_{r,2}^{2}}} & {{Eqn}.\mspace{14mu}(8)}\end{matrix}$During the third hop, relay node 130 may transmit the network-codedsignal. The signal received at base station 140 after T₃ may beexpressed as

$\begin{matrix}{{y_{1}^{(3)}(k)} = {{G_{r,1}d_{1}} + {\sum\limits_{i = 2}^{N_{b}}{G_{r,i}d_{i}}} + w_{3}}} & {{Eqn}.\mspace{14mu}(9)}\end{matrix}$

-   -   where G_(r,i) is the channel between the transmitter of the        active relay of BS i and the receiver of BS 1, and d_(i) denotes        the network-coded transmitted signal from the active relay of BS        i.        The resulting SINR, Γ₃ is then given by:

$\begin{matrix}{\Gamma_{3} = \frac{{G_{r,1}}^{2}p_{r,1}}{{\sum\limits_{i = 2}^{N_{b}}\;{{G_{r,i}}^{2}p_{r,i}}} + \sigma_{3}^{2}}} & {{Eqn}.\mspace{14mu}(10)}\end{matrix}$

-   -   where p_(r,i) is the transmitted power of the active relay in BS        i.        The transmitted network coded data may then be decoded based on        the following algorithm. Without loss of generality, let us        assume that user terminal 1 (UT 110-1) has a better link to base        station 140 than user terminal 2 (UT 110-N), i.e., Γ₁>Γ₂. Then        the data of user terminal 1 may be decoded based on its SINR        through the direct link to base station 140. However, this data        still needs to be transmitted at a rate so that it can be        decoded at relay node 130 so that it can further be used to        decode the network coded data (e.g., XOR-ed data) transmitted by        relay node 130. The resulting equivalent SINR of user terminal 1        may then be given by:        Γ′₁=min{Γ₁;Γ_(r,1)}  Eqn. (11)        Consequently, the relayed signal may then be used (after being        decoded against the transmission of user terminal 1) in order to        improve the equivalent SINR of the weak user terminal in the        pair. Assuming maximum ratio combining (MRC), the equivalent        SINR of user terminal 2 may then be given by:        Γ′₂=min{Γ₂+Γ₃;Γ_(r,2)}  Eqn. (12)        The resulting sum capacity equation may be based on the amount        of time each node is given to transmit its data.

For a “fair-per-node” time division scheme (alternatively referred to astime division “scheme 1” herein), shown in FIG. 6, the totaltransmission time T may be divided into three equal time slots given by:

$\begin{matrix}{T_{1} = {T_{2} = {T_{3} = \frac{T}{3}}}} & {{Eqn}.\mspace{14mu}(13)}\end{matrix}$One time slot may be assigned to each node, e.g., T₁ may be assigned touser terminal 1 (e.g., UT 110-1), T₂ may be assigned to user terminal 2(e.g., UT 110-N) and T₃ may be assigned to relay node 130. With suchtime slot assignments, the “strong” user terminal (e.g., the userterminal having the strongest direct radio channel connection to basestation 140) will have access to one third of the total transmissiontime T, whereas the “weak” user terminal (e.g., the user terminal havingthe weakest direct radio channel connection to base station 140) willhave access to the remaining two thirds of the total transmission time T(i.e., one third through its own transmission time, and another thirdthrough the relay node transmission time).

Based on the SINR expressions derived above, the sum capacity of the“fair-per-node” time division scheme of FIG. 6 may be expressed as:

$\begin{matrix}{C_{1} = {\frac{1}{3}\lbrack {{\log_{2}( {1 + \Gamma_{1}^{\prime}} )} + {\log_{2}( {1 + \Gamma_{2}^{\prime}} )}} \rbrack}} & {{Eqn}.\mspace{14mu}(14)}\end{matrix}$

For a “fair-per-user terminal” time division scheme (alternativelyreferred to as time division “scheme 2” herein), shown in FIG. 7, thetotal transmission time T may be divided into three time slots given by:

$\begin{matrix}{T_{1} = {{2T_{2}} = {{2T_{3}} = \frac{T}{2}}}} & {{Eqn}.\mspace{14mu}(15)}\end{matrix}$Time slot T₁ may be assigned to the “strong” user terminal, time slot T₂may be assigned to the “weak” user terminal, and time slot T₃ may beassigned to relay node 130. With the relative time division shown inFIG. 7, the “strong” user terminal and the “weak” user terminal willeach have access to half of the transmission duration T. The sumcapacity of the time division scheme of FIG. 7 may be expressed as:

$\begin{matrix}{C_{2} = {\frac{1}{2}\lbrack {{\log_{2}( {1 + \Gamma_{1}^{\prime}} )} + {\frac{1}{2}{\log_{2}( {1 + \Gamma_{2}^{\prime}} )}}} \rbrack}} & {{Eqn}.\mspace{14mu}(16)}\end{matrix}$Due to the log₂ operator in the capacity equation, it would be expectedthat time division scheme 2 may provide a comparable performance to timedivision scheme 1 at low SINR regions, whereas time division scheme 2may provide substantially higher gains at high SINR regions, thus,providing a higher total system throughput.

Time division schemes 1 and 2, described above, may be combined in someimplementations to form a cost-based algorithm. One example of such acombination is choosing the time division scheme (e.g., scheme 1 orscheme 2) that maximizes the sum-capacity at a given time period. Forexample, a time division scheme t* may be selected that maximizes thesum capacity according to the following expression:

$\begin{matrix}{t^{*} = {\underset{t \in {\{{{{Scheme}\; 1},{{Scheme}\; 2}}\}}}{argmax}{C( {U_{1},U_{2}} )}}} & {{Eqn}.\mspace{14mu}(17)}\end{matrix}$As another example, a time division scheme t* may be selected thatminimizes generated interference according to the expression:

$\begin{matrix}{t^{*} = {\underset{t \in {\{{{{Scheme}\; 1},{{Scheme}\; 2}}\}}}{argmin}{I( {U_{1},U_{2}} )}}} & {{Eqn}.\mspace{14mu}(18)}\end{matrix}$

-   -   where the interference may be measured at base stations other        than base station 140, at other relay nodes, and/or at other        user terminals.

Thus, the interference may be associated with links between the userterminals and the relay node, between the relay node and the basestation, between the user terminals and base station, etc. Exemplarycost-based algorithms, such as those represented by Eqns. (17) and (18),may permit “fairness” to be controlled through the selected timedivision scheme and a parameter (e.g., a given performance measure)associated with network coding of data transmitted between the pluralityof user terminals and the base station via the relay node to beoptimized.

FIG. 8 is a flowchart that illustrates exemplary operations associatedwith selecting a time division scheme for time dividing a transmissionresource (e.g., uplink and/or downlink in a cellular system) andallocating transmission intervals and interval lengths to user terminalsand a relay node involved in network coding based on the selected timedivision scheme. The exemplary operations of FIG. 8 may be implementedby base station 140. The exemplary operations of FIG. 8 are describedbelow with reference to the messaging diagram of FIG. 9.

The exemplary operations may begin with the receipt of link qualityinformation (block 800). The link quality information may include, forexample, Signal-to-Interference-Noise-Ratio (SINR) and/or estimates ofchannel conditions measured at one or more of UTs 110-1 through 110-N,relay node 130-1, or base station 140. For example, each of UTs 110-1through 110-N may measure a link quality associated with its link to theselected relay node (e.g., relay node 130-1 in FIG. 9) and may send thelink quality information to the selected relay node (as shown in FIG.9), or directly to base station 140. The received link quality data maypermit base station 140 to identify which of UTs 110-1 through 110-Nthat has the weakest direct radio channel connection to base station140, and identify which of UTs 110-1 through 110-N that has thestrongest direct radio channel connection to base station 140. FIG. 9depicts relay node 130-1 obtaining 910 link quality data associated withlinks to UTs 110-1 and 110-N. As further shown in FIG. 9, relay node130-1 may subsequently send link quality data 915 to base station 140.

The strength of the direct radio channel links between the userterminals and the serving base station may be determined based on thereceived link quality information (block 805). Base station 140 mayevaluate the link quality information received in block 800, which mayinclude link quality information associated with direct links betweenUTs 110-1 through 110-N, and may determine the relative strengths of thedirect radio channel inks between UTs 110-1 through 110-N and basestation 140. The user terminal with the direct radio channel link havingthe weakest strength may be referred to herein as the “weak” userterminal. The user terminal with the direct radio channel link havingthe strongest strength may be referred to herein as the “strong” userterminal. FIG. 9 depicts base station 140 determining 920 connectionstrengths of direct links between the UTs and base station 140.

A time division scheme may be selected from multiple time divisionschemes for time dividing the uplink and/or downlink based on thedetermined channel link strengths (block 810). The multiple timedivision schemes may include, but are not limited to, the“fair-per-node” scheme (scheme 1) and/or “fair-per-user terminal” scheme(scheme 2), described above. The multiple time division schemes mayinclude, but are not limited to, the “fair-per-node” scheme (scheme 1)and/or “fair-per-user terminal” scheme (scheme 2), described above. Theplurality of time division schemes may further include a time divisionscheme that attempts to equalize delay per user terminal. The multipletime division schemes may include other time division schemes that are,for example, based on channel quality measures of different links in thesystem. For example, the other time division schemes may be based onchannel quality measures associated with the links between the userterminals and the relay node, between the relay node and the basestation and/or between the user terminals and the base station.

Selection of a time division scheme may, in some implementations,include choosing a time division scheme that optimizes a performancemeasure (e.g., a parameter associated with the network coding process).For example, as expressed in Equations (17) and (18) above, a timedivision scheme (e.g., scheme 1 or scheme 2) may be selected thatmaximizes a sum capacity and/or minimizes a generated interference. Thedetermined channel link strengths (block 805) may be used in block 810to identify user terminals 110-1 through 110-N as a “weak” user terminalor a “strong” user terminal for purposes of allocating transmissionintervals and interval lengths, as shown in FIGS. 6 and 7, and asdescribed below with respect to block 815. FIG. 9 depicts base station140 selecting 925 a time division scheme from multiple time divisionschemes based on determined link connection strengths.

Transmission intervals and interval lengths may be allocated to each ofthe user terminals and to the relay node based on the selected timedivision scheme (block 815). As already described above with respect toFIG. 6, if a “fair-per-node” time division scheme (scheme 1) isselected, the total transmission time T may be divided into three equaltime slots

$( {T_{1} = {T_{2} = {T_{3} = \frac{T}{3}}}} )$where one time slot may be assigned to each node, e.g., T₁ may beassigned to user terminal 1 (e.g., UT 110-1), T₂ may be assigned to userterminal 2 (e.g., UT 110-N) and T₃ may be assigned to relay node 130-1.With such time slot assignments, the “strong” user terminal (e.g., theuser terminal having the strongest direct radio channel connection tobase station 140) will have access to one third of the totaltransmission time T, whereas the “weak” user terminal (e.g., the userterminal having the weakest direct radio channel connection to basestation 140) will have access to the remaining two thirds of the totaltransmission time T (i.e., one third through its own transmission time,and another third through the relay node transmission time).

As further described above with respect to FIG. 7, if a “fair-per-userterminal” time division scheme (scheme 2) is selected, the totaltransmission time T may be divided into three

$( {T_{1} = {{2T_{2}} = {{2T_{3}} = \frac{T}{2}}}} ),$time slots where time slot T₁ may be assigned to the “strong” userterminal, time slot T₂ may be assigned to the “weak” user terminal, andtime slot T₃ may be assigned to relay node 130-1. With the relative timedivision shown in FIG. 7, the “strong” user terminal and the “weak” userterminal will each have access to half of the transmission duration T.FIG. 9 depicts base station 140 allocating 930 transmission intervalsand interval lengths to the UTs and the selected relay node based on theselected time division scheme.

A message(s) may be sent to inform the user terminals and the relay nodeof their respective allocated transmission intervals and intervallengths (block 820). The notification message may be sent to relay node130-1 for relaying to user terminals 110-1 through 110-N, or messagesmay be sent individually to relay node 130-1, and directly to UTs 110-1through 110-N that inform the user terminals and relay node of theirrespective transmission intervals allocated in block 815. FIG. 9 depictsbase station 140 sending an exemplary notification message 935 to relaynode 130-1. Relay node 130-1 may, subsequently, relay notificationmessage 935 on to UTs 110-1 through 110-N (not shown). Subsequent to theexemplary operations of FIG. 8, relay node 130-1 may network code datatransmissions from UTs 110-1 through 110-N, based on the transmissiontime intervals and interval lengths allocated during the exemplaryoperations of FIG. 8, as generally described above with respect to FIG.5.

The foregoing description of implementations provides illustration anddescription, but is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Modifications and variationsare possible in light of the above teachings, or may be acquired frompractice of the invention. For example, while a series of blocks hasbeen described with regard to FIG. 8, the order of the blocks may bemodified in other implementations consistent with the principles of theinvention. Further, non-dependent blocks may be performed in parallel.

Aspects of the invention may also be implemented in methods and/orcomputer program products. Accordingly, the invention may be embodied inhardware and/or in software (including firmware, resident software,microcode, etc.). Furthermore, the invention may take the form of acomputer program product on a computer-usable or computer-readablestorage medium having computer-usable or computer-readable program codeembodied in the medium for use by or in connection with an instructionexecution system. The actual software code or specialized controlhardware used to implement the embodiments described herein is notlimiting of the invention. Thus, the operation and behavior of theembodiments were described without reference to the specific softwarecode—it being understood that one of ordinary skill in the art would beable to design software and control hardware to implement the aspectsbased on the description herein.

Furthermore, certain portions of the invention may be implemented as“logic” that performs one or more functions. This logic may includehardware, such as an application specific integrated circuit or fieldprogrammable gate array, or a combination of hardware and software.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the invention. In fact, many of these features may becombined in ways not specifically recited in the claims and/or disclosedin the specification.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, components or groups but does not precludethe presence or addition of one or more other features, integers, steps,components or groups thereof.

No element, act, or instruction used in the present application shouldbe construed as critical or essential to the invention unless explicitlydescribed as such. Also, as used herein, the article “a” is intended toinclude one or more items. Where only one item is intended, the term“one” or similar language is used. Further, the phrase “based on” isintended to mean “based, at least in part, on” unless explicitly statedotherwise.

What is claimed is:
 1. A method implemented at a base station in awireless network comprising first and second user terminals and a relaynode configured to relay data transmissions from the first and seconduser terminals to the base station, the method comprising: determiningqualities of links between the user terminals and the base station;selecting a time division scheme from a plurality of time divisionschemes based on the determined qualities of the links, the timedivision schemes including time slots assigned to the first and seconduser terminals and the relay node, wherein the plurality of timedivision schemes includes: (i) a first time division scheme in whichtransmission time is divided into three equal slots with: a first equalslot assigned to the first user terminal, a second equal slot assignedto the second user terminal, and a third equal slot assigned to therelay node, and (ii) a second time division scheme in which transmissiontime is divided into three distinct slots with: a first distinct slotassigned to the first user terminal, a second distinct slot assigned tothe relay node, and a third distinct slot, equal to a combined timeinterval of the first and second distinct slots, assigned to the secondterminal; allocating, based on the selected time division scheme,transmission intervals and interval lengths to each of the first andsecond user terminals and the relay node; notifying the user terminalsand the relay node of their respective allocated transmission intervalsand interval lengths; and receiving from the relay node network-codeddata transmitted to the base station based on the allocated transmissionintervals and the interval lengths.
 2. The method of claim 1, where thequalities of the links include signal to noise and interference ratiosassociated with the links between the user terminals and the basestation.
 3. The method of claim 1, further comprising determining linkqualities associated with links between the user terminals and the relaynode, and wherein selecting the time division scheme is further based onthe determined links qualities associated with links between the userterminals and the relay node.
 4. The method of claim 3, furthercomprising determining a link quality associated with a link between therelay node and the base station, and wherein selecting the time divisionscheme is further based on the determined link quality associated withthe link between the relay node and the base station.
 5. The method ofclaim 1, wherein the first distinct slot of the second time divisionscheme is equal to the second distinct slot of the second time divisionscheme.
 6. The method of claim 1, wherein the plurality of time divisionschemes further includes a third time division scheme that achievesequal delay per user terminal.
 7. The method of claim 1, whereinselecting the time division scheme comprises selecting the time divisionscheme that maximizes a sum capacity value.
 8. The method of claim 1,where selecting the time division comprises selecting the time divisionscheme that minimizes generated interference associated with at leastone of the relay node, the base station, and the user terminals.
 9. Abase station configured to serve a plurality of user terminals via arelay node in a cell of a wireless network, the base station comprising:a link quality analysis unit configured to determine qualities of linksbetween the plurality of user terminals and the base station, a timedivision scheme selection unit configured to select, based on thedetermined link qualities, a time division scheme from a plurality oftime division schemes, the time division schemes including time slotsassigned to the first and second user terminals and the relay node,wherein the plurality of time division schemes includes: (i) a firsttime division scheme in which transmission time is divided into threeequal slots with: a first equal slot assigned to the first userterminal, a second equal slot assigned to the second user terminal, anda third equal slot assigned to the relay node, and (ii) a second timedivision scheme in which transmission time is divided into threedistinct slots with: a first distinct slot assigned to the first userterminal, a second distinct slot assigned to the relay node, and a thirddistinct slot, equal to a combined length of the first and seconddistinct slots, assigned to the second terminal; a transmissionallocation unit configured to allocate, based on the selected timedivision scheme, the assigned slots to each of the plurality of userterminals and to the relay node, the allocated slots associated with atleast one of an uplink and downlink; and a notification message unitconfigured to notify the plurality of user terminals and the relay nodeof their respective allocated slots.
 10. The base station of claim 9,wherein the qualities of the links include signal to noise andinterference ratios associated with links between the user terminals andthe base station.
 11. The base station of claim 9, wherein the firstdistinct slot of the second time division scheme is equal to the seconddistinct slot of the second time division scheme.
 12. The base stationof claim 9, wherein the plurality of time division schemes furtherincludes a third time division scheme that achieves equal delay per userterminal.
 13. The base station of claim 9, wherein the time divisionscheme selection unit is configured to select the time division schemethat maximizes a sum capacity value.
 14. The base station of claim 9,wherein the time division scheme selection unit is configured to selectthe time division scheme that minimizes generated interferenceassociated with at least one of the relay node, the base station, andthe user terminals.
 15. The base station of claim 9, wherein the linkquality analysis unit is further configured to determine link qualitiesassociated with links between the user terminals and the relay node, andwherein the time division scheme selection unit is configured to selectthe time division scheme further based on the determined link qualitiesassociated with links between the user terminals and the relay node. 16.The base station of claim 15, wherein the link quality analysis unit isfurther configured to determine a link quality associated with a linkbetween the relay node and the base station, and wherein the timedivision scheme selection unit is configured to select the time divisionscheme further based on the determined link quality associated with thelink between the relay node and the base station.